1. Field of the Invention
The invention relates to a volume meter, specifically for the measuring of the volume of cups in a printing device, comprising a foil, fastening agents for temporary fastening of the foil on a screen, a reservoir that is connected during operation with a space between the foil and a screen, and a viscous substance present in the reservoir.
Here a printing device is understood to mean a device for applying for example ink, a coating, glue for example on paper, or any other desired base. A printing device often has a screen roller. The cups are located in the casing of the roller. A screen roller is engraved by means of a moulette on a steel roller or by means of a laser if the roller is coated with a ceramic coating. There are also other printing devices, for example those in which the printing process takes place with the aid of a flat die. Here the cups are in the printing surface of the die. The volume of the cups is important to the printing process, amongst other reasons to determine how much printing ink can be fed during the printing process.
Foil is understood to mean any substrate that is thin and flexible, irrespective of what material it consists of, whether this is for example plastic or paper. The specified space between the foil and the screen roller is only present during the spreading of the viscous material. Before this and after the viscous substance is spread in the cups the foil is preferably against the screen.
2. Prior Art
A volume meter for measuring the volume of cups in a printing device is known from American patent U.S. Pat. No. 5,235,851. The known volume meter comprises a foil, which on its underside has an adhesive layer, which has two adhesive strips between which a channel is formed. This adhesive layer serves to bring the foil on a screen to be measured. In the reservoir there is a liquid and in order to keep this liquid in the reservoir the reservoir is closed off by another foil, which is fastened to the foil along a closed connection zone around the indentation.
In this known volume meter the measurement takes place by placing the foil on the screen and then passing a doctor blade along the foil, so that the liquid in the reservoir is pressed against a weakening in the connection zone and the weakening is broken through. Then the doctor blade is passed along the foil, at which time the liquid is forced into the channel. The liquid is spread in the cups, with the length of the surface of the liquid-filled cups being a measure for the volume of the cups.
A disadvantage of this known volume meter is that the accuracy of the measurement leaves something to be desired.
An objective of the invention is to provide a volume meter of the type described in the preamble with which a higher accuracy can be achieved in the measurement of the volume than with the known volume meter. To this end, the volume meter according to the invention is characterised in that the foil is free of the fastening agents over an area, which area is larger than a spot that the viscous substance covers after the spreading of the viscous substance from the reservoir, between the foil and the screen to be measured, in the cups.
It has been noted that in the known volume meter the liquid in the reservoir during scraping sometimes comes under the glue layer of the limitations of the channel. By only pressing the foil outside the efflux opening in the reservoir against the screen or keeping it stretched, the viscous substance can go in all directions unhindered and the viscous substance is not forced through a channel determined in advance. So the viscous substance can also not go undesired under the adhesive outside a channel. It has been noted that during scraping the viscous substance always shows the same pattern on the screen (the form is roughly that of a pinecone). For determining the surface of the pattern it is therefore sufficient to measure the length of the pattern.
An embodiment of the volume meter according to the invention is characterised in that the reservoir is formed by an indentation in the foil. Preferably, the indentation has such a form that the foil does not fold double, if the foil is applied to a screen and a doctor blade is passed along the indentation in order to bring the viscous substance out of the reservoir, so that the foil at the location of the indentation is pressed by the doctor blade against the screen.
In the known volume meter the indentation has such a form that during the passing of the doctor blade along the indentation the foil folds double. However, it has been noted that by the double folding viscous substance always stays behind in the reservoir, which remains enclosed in the double folded portion of the foil. By a suitable form of the indentation, which can easily be experimentally found, for example a rather flat indentation, the foil does not fold double. The suitable form of the indentation depends partly on the stiffness and the thickness of the foil used.
It is noted that this latter embodiment, in which the indentation has such a form that during scraping the foil cannot be folded double, can also be used without the characteristic that the foil over a sufficient area is free of the fastening agents. For example, this form of indentation, for example used with the known volume meter, also results in an improvement of accuracy since little or no viscous substance remains behind in the reservoir during scraping. For this reason the possibility is specifically kept open of claiming this characteristic (form of indentation) independently of the main characteristic (area free of fastening agents).
To prevent the viscous substance from coming undesired out of the reservoir during use, a further embodiment of the volume meter is characterised in that the volume meter also comprises a further foil, which is present on a portion of the foil and covers the indentation.
When the viscous substance is spread out of the reservoir with the known volume meter, first a connection zone must be broken through by pressing the viscous substance against a weakening in the connection zone. To simplify the pressing of the viscous substance out of the reservoir, another embodiment of the volume meter is characterised in that the further foil is fastened to the foil with an adhesive, with the adhesive partly being present around the indentation and a strip between an edge of the) further foil and the indentation being free of adhesive. The viscous substance can be pushed via this strip out of the reservoir without pressure needing to be built up in the viscous substance.
The fastening agents with which the volume meter can be placed on a screen preferably comprise another adhesive, which is present on a portion of the foil and at least on a portion of the further foil. Preferably, the further foil at the location of the reservoir has the further adhesive. For this the reservoir is well fixed on the screen and the viscous substance can be spread out of the reservoir well.
To improve how the volume meter can be handled, yet another embodiment is characterised in that the volume meter also comprises a removable cover foil, which covers the further adhesive present on the foil and the further foil.
The standards that the viscous substance in the reservoir must fulfil are: it must be well doseable, it must not evaporate too much to be able to guarantee a long storage time between manufacture and use, it must be able to be properly placed in the cups, and it must be visible.
An embodiment of the volume meter that fulfils these standards is characterised in that the viscous substance comprises grease and/or oil. Preferably, the main ingredient of the viscous substance is grease.
To improve its visibility on a screen the viscous substance preferably comprises a colorant. The composition of the viscous substance is preferably approximately 1 weight per cent colorant and approximately 99 weight per cent grease. However, a composition of approximately 0.5 weight per cent colorant, approximately 10 weight per cent oil and approximately 89.5 weight per cent grease is also good.
The oil is preferably mineral motor oil for petrol and LPG motors for all seasons, preferably 15W-40 oil. The grease is preferably Keenol grease, and the colorant is preferably Waxoline.
In the above described characteristics and embodiments of the invention the word screen is understood to mean not only a screen of cups of a printing device, but also other screens, for example a surface of which the roughness should be determined with the aid of the volume meter according to the invention. In that case cups is understood to mean the valleys in the roughness profile of the surface.